This invention relates to apparatus for measuring the pH of a solution, particularly for preventing contamination of the pH probe thereof, and more particularly to preventing contamination of the probe and providing means for flushing the probe which additionally serves to check that the probe is functional.
Environmental regulations require measuring the pH of solutions such as sanitary and storm sewer effluents. It is desirable to measure the pH right in the stream. Generally, such streams are loaded with contaminants such as oil, grease, paint, micro-organism growth, etc. Apparatus for measuring the pH of such streams utilize electrodes enclosed in a sensitive glass wherein hydrogen ions migrate through the glass pores, whereby a readout of the pH is provided. These glass-type pH probes provide quick response to changes in effluent pH. The probe glass becomes coated or fouled by the contaminants, whereby the hydrogen ions can no longer migrate through the glass. Thus, to provide effective pH monitoring, it is necessary to remove the coating on the glass caused by the contaminants.
Various schemes have been tried in an effort to prevent fouling of pH probes. For example, it has been proposed to provide a scrubbing or wiping mechanism which would remove the accumulation as it is collected on the probes. Attempts were also made at cleaning the probes by high-flow velocities, ultrasonic cleaning, and also by periodically cleaning with steam. Also, filtering of the solution prior to contact with the probe has been utilized. The schemes have proved to be ineffective and, in many instances, require a substantial amount of down-time of the monitoring system, as well as costs of the cleaning arrangements. In addition, many probes must be recalibrated whenever cleaned or removed for cleaning, thus causing continuous monitoring and calibration by technical personnel. These prior approaches are exemplified by the following:
U.S. Pat. No. 3,290,584, issued Dec. 6, 1966, to Van Dewisen Harms et al., discloses a pH probe mounting assembly incorporating a filter means. Liquid enters an overflow chamber and passes through a sheet of filter paper prior to its entering a pH probe containing c chamber. The filter paper is continuously rolled so that a fresh portion of paper continuously filters the liquid.
U.S. Pat. No. 3,440,525, issued Apr. 22, 1969, to C. P. Cardeiro, discloses a pH-sensitive electrode that minimizes errors due to drifts by providing a substantial excess of undissolved salt crystals immersed in a saturated salt bridge solution communicable, by numerous capillaries, between chambers, one of which contains the test solution.
U.S. Pat. No. 4,151,255, issued Apr. 24, 1979, to I. A. Capuano et al. discloses an apparatus for measuring the pH of a sample. The apparatus has a rinse and buffer standardization system and is used to automatically and periodically standardize the pH measuring means.
Thus, a need exists to prevent the current rapid contamination of pH probes and for reducing the time period for the required periodic checking of the function of such probes. Further, there is a need for a pH probe assembly that can be inserted directly into a contaminated stream.